Radiation detectors for detecting high energy photons (e.g., gamma (γ) rays and X-rays) are well-known in the art and are used to detect high energy photons produced by any of a wide range of radioactive materials or other types of samples. The detection, identification, and spectroscopy of such energetic photons comprises an integral part of the fields of nuclear and particle physics as well as several fields that make use of radioactivity, including, for example, medicine, forensic science, and industrial inspection applications. Radiation detectors are also used at nuclear power plants and laboratories to monitor and study radiation.
Ionizing radiation detectors, such as gamma (γ) ray detectors, can be classified into one of two types depending on the apparatus that is used to detect the high energy photons. The first type, referred to herein as “gas tube” or simply “gas” detectors utilizes a gas-filled chamber or tube which contains a positively charged wire. When a high energy photon enters the chamber it may ionize a gas atom, causing it to release an electron or electrons in the process. The liberated electron or electrons may in turn ionize additional gas atoms, which liberate yet more electrons. The liberated electrons are collected by the positively charged wire. A detection circuit connected to the wire measures the charged delivered to the wire by the electrons. Generally speaking, the higher the energy of the incoming photon, the more atoms are ionized and the more electrons are liberated. Therefore, the magnitude of the detected charge is generally related to the energy of the incoming photon.
Solid state detectors are similar to gas detectors described above except that the active volume (i.e., the gas) is replaced by a semiconducting material, such as germanium, although other materials may be used. Accordingly, both types of detectors have in common the property that they use the energy of the incoming photon to ionize an atom of some material. Generally speaking, solid state detectors provide superior sensitivity and resolution compared with gas tube detectors, although both types remain in use.
Besides high energy photons, radiation can also comprise high energy particles, such as alpha (α) particles, beta (β) particles, and neutrons (n). Such high energy particle-type radiation is usually detected by other types of detectors. For example, neutrons are typically detected by using a radiator or converter which absorbs incoming neutrons and radiates charged particles. The radiated particles may then be detected by means of an ionizing type radiation detector of the type described above.
While radiation detectors for detecting high energy photons (e.g., gamma rays) and high energy particles (e.g., neutrons) exist and are being used, they are not without their problems. For example, a problem with prior art neutron detectors relates to the sensitivity of the detectors to gamma rays. Consequently, it is difficult for such detectors to discriminate (i.e., differentiate) between gamma rays and neutrons. Since both gamma and neutron radiation must be separately measured in order to accurately measure the radiation field, such neutron detectors are not particularly useful in accurately characterizing the radiation field.
One way to solve the problem of simultaneously measuring both gamma and neutron radiation is to utilize two separate detectors, one optimized for gamma ray detection and the other optimized for neutron detection. While such dual detector systems are known and have been used, they tend to be bulky, heavy, and difficult to carry. In addition, such devices tend to consume a fair amount of electrical power, thus limiting their usefulness, particularly in portable applications. While smaller, more portable detectors exist, they are typically only responsive to one type of radiation. Therefore, a user must carry two separate detectors if it is desired to monitor both gamma radiation and neutron radiation.